In applicant's prior U.S. Pat. No. 3,332,327, there is disclosed a pavement marker adapted to be placed on highways and in which the pavement marker front face is inclined at a predetermined angle to the roadway surface so that a self-cleaning effect is provided by virtue of that predetermined angle, whereby that pavement marker achieves initial high optical efficiency and the optical deterioration arising out of contact with tires of oncoming vehicles is substantially reduced by allowing the face to be periodically wiped clean by contact with such vehicles. In addition, there is disclosed in that patent a cube-corner reflex reflective optical system in which the cube axes of the cube-corner reflective elements are inclined so as to be substantially coincidental with the nominal incoming refracted ray. Pavement markers made in accordance with the '327 patent and similar to the structure disclosed therein have been extremely successful in operation, and several millions of them have been installed, primarily in areas where no snowplowing of the roads is required. That earlier pavement marker, while highly effective as a nighttime signal, is substantially ineffective as a daytime marker, because of the nature of its construction, and, in particular, the large metallized area of the reflective portion thereof, which metallizing is required because of the epoxy fill. Also, the height of the earlier pavement marker precluded its practical use under snowplow conditions.
Furthermore, the '327 marker involves a tradeoff between abrasion-resistance and self-cleaning or wiping characteristics whereby given the materials used there are limits to the improvement that can be made in one quality without adversely affecting the other.
Also, where a road is constructed of a particular material, or is newly installed asphalt, the '327 marker has caused deterioration of the road surfaces. Some users have recommended delaying installation of such markers for a year to allow the road to cure. In an attempt to overcome these problems caused by unsatisfactory road surfaces or newly installed surfaces, the '327 markers were installed with an impact-absorbing pad. However, the use of the impact-absorbing material still did not completely resolve the problem.
In applicant's prior U.S. Pat. No. 3,833,285, issued Sept. 3, 1974, there is disclosed an optical system for use with cube-corner-type reflectors, wherein the reflectivity of the reflector is increased by enlarging one of the three dihedral angles forming the cube-corner element, thereby improving the visibility of the reflector at a selected wider observation angle. Applicant presently has on file a United States Application Ser. No. 753,132, filed Dec. 22, 1976, a continuation of application Ser. No. 625,723, now U.S. Pat. No. 4,032,319 filed Mar. 24, 1967, which discloses a cellular system for reflectors in which, in one embodiment, a cellular reflector member is provided on an underlying metal casting for providing a snowplow-type marking. That reflector design is capable of increased daylight reflectivity. Applicant also is aware of pavement markers used on the roadway and put out by Ray-O-Lite, Inc., of Huntington Beach, California, and identified on the shell thereof as a model "FLD", in which three substantially large cells are provided, the cells being provided by walls which extend beyond the apices of the cube-corner elements and in which the lens member is affixed to a substantially flat support wall lying thereunder. These prior markers presented an undesirable high profile and other disadvantages.